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My Packs: (WIZEPREP) (BIOCHEM 2280) > Chapter 4: 4.4 Characteristics of Membrane Proteins > Flashcards

Chapter 4: 4.4 Characteristics of Membrane Proteins Flashcards

1
Q

What are the two types of proteins in the lipid bilayer?

A
  • Peripheral
  • Integral
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2
Q

Define:

Glycoproteins

A

Proteins with lipid post-translational modifications that aid in membrane insertion and cell recognition

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3
Q

What are the two types of integral proteins?

A
  1. Transmembrane
  2. Monotopic
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4
Q

List:

Ways peripheral membrane proteins can be attached to the membrane

A
  1. Amphipathic helices
  2. Hydrophobic loop regions
  3. Attachment to integral proteins
  4. Ionic and H-bonds
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5
Q

What are the methods to remove peripheral membrane proteins?

A
  1. High salt method
  2. pH change
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6
Q

Describe:

Removal of Peripheral Membrane Proteins via High salt method

A
  • Neutralizes or “shields” charges using ions in salt
  • Breaks hydrogen bonds and ionic interactions
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7
Q

Describes:

Removal of Peripheral Membrane Proteins via pH change

A
  • Protonates/deprotonates charged amino acids
  • Breaks hydrogen bonds and ionic interactions
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8
Q

Define:

Integral Membrane Proteins

A

Completely span the membrane

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9
Q

How many types of integral membrane proteins are there?

A

6

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10
Q

Describe:

Each type of integral membrane proteins

A
  1. Type I: Single pass amino group (NH3+) on outside
  2. Type II: Single pass amino group (NH3+) on inside
  3. Type III: Single protein with multiple passes
  4. Type IV: Multiple proteins each with single passes
  5. Type V: Held to membrane via lipid anchor
  6. Type VI: Held to membrane via trans-membrane segment and lipid anchor
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11
Q

What are the regions of the cellular membrane?

A
  1. Extracellular-facing region
  2. Membrane spanning regions
  3. Intracellular-facing region
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12
Q

State:

Purpose of Extracellular-facing region

A

Play roles in signalling, transport, and cell recognition and communication (Lipids and glycosylated proteins)

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13
Q

State:

Purpose of Membrane spanning regions

A

~20 amino acids long and mostly hydrophobic

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14
Q

State:

Purpose of Intracellular-facing region

A

Transmit signals to the cytosol through “tails” and are involved in transport

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15
Q

How are integral membrane proteins removed?

A

Requires harsh removal (detergents or organic solvents)
* Detergents separate proteins from lipids

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16
Q

How is amino acid hydrophobicity measured?

A
  1. Partitioning method
  2. Surface exposure
17
Q

In the partitioning method:

How is amino acid hydrophobicity measured?

A

Observe amino acid distribution between organic solvent (non-polar) and aqueous solvents (polar)

18
Q

In the partitioning method:

What are two solvents used to mimic conditions for the partitioning methods?

A
  1. n-octanol (non-polar): Close to conditions of membrane interior
  2. Water (polar): Close to conditions of cytosol
19
Q

State:

The formula for partition coefficient

A

P(AA) = C(AA nonpolar) / C(AA polar)

20
Q

True or False:

The partition coefficient is reported as the formula

A

Not exactly, often reported as log of this value

21
Q

Are polar or non-polar amino acids found on the surface of proteins?

A

Polar

22
Q

Are polar or non-polar amino acids found in the interior of proteins?

A

Non-polar

23
Q

The average accessibility of each amino acid is determined by…

A

From the coordinates of 12 model globular proteins

24
Q

What is hyrdropathy calculated as in surface exposure?

A

As the fraction of the total number of the protein that is at least 95% buried from the surface

25
Q

Describe:

The process of Assigning Transmembrane Sequences based on Hydropathy

A
  1. Assign hydropathy value to each residue in the protein (either a positive or negative value) - using Kyte-Doolittle Hydropathy scale
  2. In a series of 7 residues the average of the seven values is assigned to amino acid in position 4
  3. Move over one residue and perform calculation
  4. Plot on grid
26
Q

What is a problem when trying to span the non-polar membrane?

A

The polar backbone

27
Q

How is a non-polar membrane spanned?

A

Typically form alpha-helix 20-25 amino acids long to span 3-4 nm membrane

28
Q

True or False:

100% of single spanning proteins utilize the alpha-helix

A

True

29
Q

Besides the polar backbond in a non-polar membrane, what is another issue in membrane protein folding?

A

The fact that most hydrophobic residues have a higher propernsity to form beta-sheets

30
Q

Hydrophobic resides having a higher propensity to form beta sheets is based on…

A

Chou-Fasman parameters

31
Q

Due to hydrophobic residues:

The need to neutralize ——– and ————– are a higher priority and supersede these ———-

A
  1. Backbone
  2. Hydrophobicity
  3. Parameters
32
Q

What do most transmembrane proteins contain? Why?

A

Often contain Gly
* For helix-helix interactions
* As most transmembrane proteins span the membrane multiple times

My Packs: (WIZEPREP) (BIOCHEM 2280) (19 decks)

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